A woman with a genetic disease marries a man who does not carry the disease. It is not possible for their children to carry the disease. The disease must be
a) sex - linked
b) recessive
c) dominant
d) cause by an extra chromosome
my answer is recessive
To carry the disease means that it is in the genotype but not the phenotype. That would happen with a recessive gene. It will occur.
To determine the correct answer, let's understand the possibilities based on the information provided.
When a woman with a genetic disease marries a man who does not carry the disease, we can infer that if the disease were dominant or caused by an extra chromosome, their children would have a possibility of inheriting the disease. This is because these types of disorders would be expressed even if only one parent carries the disease-causing allele.
Therefore, option c) dominant and option d) caused by an extra chromosome can be eliminated.
Now, the fact that their children cannot carry the disease suggests that it cannot be a sex-linked condition. Sex-linked disorders are caused by genes located on the sex chromosomes (X and Y), and the inheritance pattern can cause certain conditions to be more prevalent in one gender or the other. However, even if a man did not carry a specific sex-linked gene, his daughters could still be carriers for it.
Therefore, option a) sex-linked can also be eliminated.
This leaves us with the conclusion that the disease must be recessive. In this case, both parents would need to carry the disease-causing allele in order for their children to be affected. As the man does not carry the disease, their children would not inherit the disease-causing allele, resulting in their inability to carry the disease.
Hence, your answer of recessive (option b) is correct.